1. Field of the Invention
An external control device for wirelessly controlling an implantable medical device, and in particular, to a universal or common external control device for use by multiple conditional access users each of which has varied access to functionality of the implantable medical device.
2. Description of Related Art
When controlling an implantable medical device it is often desirable to limit or restrict access of certain functionality to specific users. For example, in the case of a device for the dispensing of fluid medication it is imperative that the patient be restricted in the volume of medication to be dispensed; otherwise, serious health risks or possible drug dependency may result.
U.S. Pat. No. 6,126,642 is directed to a patient controlled intravenous fluid dispenser for controllably dispensing fluid medicament, e.g., pain killing drugs, intravenously at a selected uniform rate. To positively regulate the patient administration of the medicament, the dose intervals at which a selected medicament can be administered, as well as the volume of the dose of the medicament to be administered, is preset only by an authorized person such as the treating physician and, once set, cannot be altered by the patient. The device setting can only be operated or adjusted by an all mechanical mechanism, i.e., by a small physical physician's key that remains in the possession and control of the treating physician or health care worker. Specifically, the patented patient controlled analgesia device has dispensing means that includes two manually rotatable control knobs 34, 37, one of which is used to control the dose volume while the other is used to adjust the dose interval. Both rotating knobs are carried by a common operating rod. Locking means are provided for preventing rotation of control knobs 34 and 37 unless and until a locking rod, which comprises a part of the locking means, is moved from a locked position to an unlocked position via a locking key inserted into the device. In the locked position the locking rod prevents rotation of the control members. However, when the locking rod is slid to its unlocked position the control knobs can be freely rotated by the treating physician to precisely preset the volume of each dose of medicament to be delivered and preset the interval between doses.
A physical locking key having all mechanical parts is possible in the patented system because the intravenous fluid dispenser and its control knobs are located externally of the patient's body. In the case of an implantable medical device controlled wireless by an external control device, an all mechanical construction such as that in the patented system would not be possible since the control knobs on the external device have no physical interaction with the parts of the implantable medical device.
In the patented intravenous fluid dispenser, access to a single level of functionality (e.g., adjustment of the control knobs) is varied between one of two states (unlocked/accessible state versus locked/prohibited state). The system is therefore designed to only distinguish or restrict access of a single set or class of functions (e.g., adjustment of the control knobs) between these two states. By default, when the locking rod is in the first locked position patient adjustment of the control knobs is prohibited. It is only when the locking key is physically inserted into the device and the locking rod is slid to its second unlocked position (unlocked/accessible state) that the controls knobs can be rotated by the treating physician. Therefore, the patented patient controlled intravenous fluid dispenser is only suitable for a single user, e.g., the physician, having conditional access. In alternative applications, apart from the patient, conditional access to particular functionality may be warranted by more than one user. For instance, it is possible that users other than the physician should be able to adjust the control knobs but also be provided access to functionality that otherwise may remain prohibited by the physician. Modification of the patented device to accommodate multiple conditional access users having access to varied, but sometimes overlapping, functionality would require a physical key for each function to mechanically prohibit or permit access to the particular activity. In the case of more than one function this would disadvantageously require each conditional access user to carry multiple keys, wherein each key has a unique physical design to mechanically unlock parts associated with a single function.
It is therefore desirable to design a universal external control device for wireless control of an implantable medical device whose functionality is conditionally accessible by multiple conditional access users, without the use of multiple keys one for each function or a mechanical locking mechanism associated with the implantable medical device.